Using Blair to spec a Cam

[SchmidtMotorWorks]

Jon,
Just what does Blair's calculation telling me?

I am understanding to tell me what time area I need for a give BMEP.

So how would you do it?

Stan

1. Vannik has already worked it out nicely in the image shown above; the UI should look like that.

2. Computing the target values from Blairs paper is straight forward, no need to explain that part .

3. As Vannik and I mentioned, the values used in Blairs concept were few but over a wide range of engines.
You will want to make it possible to edit and save those values so that the concept can be fine tuned to whatever type of engines one is working on.

4. You will need to choose some method of modeling a reasonable lift curve.
The most valuable way to do that will be to work with a cam company that will provide about 10-20 points along the lift curve. That way you can easily interpolate the points in between and then choose from those cams and adjust the index of the lobes to meet the targets.

[Stan Weiss]

Jon,
I can already take a number of points from a cam and generate a simulated lift file (every .1, 1, 2, or 5 degrees) using either polynomials or splines.

I can take valve size, rpm, rocker arm ratio, and the file file and calculate the time area.

I think you keep missing the point of what I am trying to do here.

Stan

[SchmidtMotorWorks]

Jon,
I can already take a number of points from a cam and generate a simulated lift file (every .1, 1, 2, or 5 degrees) using either polynomials or splines.

I can take valve size, rpm, rocker arm ratio, and the file file and calculate the time area.

I think you keep missing the point of what I am trying to do here.

Stan

Then just match it to the targets and you are done.

[vannik]

Stan,

The way I understand what you want to do is correct. The value is a "normalized" value and you have to "de-normalize" it for the specific engine you want to do the cam profile for.

I must admit I have never thought of doing it this way - very interesting!

One thing people seem to disregard about Blair - he was focused on designing an engine from scratch and giving the designer guidance to start with realistic values. The aim was not to wring the last 0.5% power out of an existing engine.

[maxracesoftware]

Stan
I am trying to use Blair's and time area.
Nowhere's does it need flow numbers.
Sorry, I just looked and the head I would use on this example
has a 2.23" intake valve (432 cfm @ .800")
and while I am correcting myself the exhaust valve is 1.72".

Stan ,
your Compression Ratio + VE% + Head CFM is already included ( sort of hidden inside )...
inside your desired 900 Peak HP at 7500 RPM
and inside your Peak TQ = 630.24 ( BMEP = 177.645 )

535 ci Pontiac engine for this example.
bore = 4.350", stroke = 4.500", rod = 6.700", cr = ??? (Pump gas), ( i used 10.25 and 11.0:1 CR )
Intake Valve = 2.230", Exhaust Valve = 1.720"

Maximum Head CFM @28in. = 431.99999455 to 462.61053223 CFM at 111.62117 % VE
Maximum Piston CFM = 962.46928032 occurs at 73.077765 degrees ATDC
Minimum recommended Flowbench Test Pressure = 62.4 inches vertical Manometer Water Column

Maximum Piston Velocity = 9325.689975 FPM occurs at 73.077765 degrees ATDC
Average Piston Velocity = 5625.000000 in Feet Per Minute
Piston Depth at 73.077765 degree ATDC= 1.950290 inches Cylinder Volume = 474.9729 CC
Crank Angle at which Rod and Crank axis form a 90 degree angle = 71.4368729 ATDC
Maximum TDC Rod Tension GForce = 4802.0155 G's Acceleration Ft/Sec^2 = 154500.2788
Maximum BDC Rod Compression GForce = 2387.5943 G's Acceleration Ft/Sec^2 = 76818.5744

i get these minimum Cam Specs : (* Race only Engine with 10.25:1 CR )
0.8617 = Intake Valve Lift 278.0 Duration @0.050"
0.8334 = Exhaust Valve Lift 298.0 Duration @0.050"
LSA = 108.118 degrees
* Specs adjusted for ValveTrain Deflection = 0.0000 Intake Lash= 0.0250 Exhaust Lash= 0.0250
.... * minimum Cam Specs required to achieve 900 Peak HP @ 7500 RPM

i get these maximum Cam Specs : (* Professional Race only Engine with 11.0:1 CR )
0.97059 = Intake Valve Lift 284.0 Duration @0.050" ( Time-Area = 0.9569 Lift )
0.90592 = Exhaust Valve Lift 300.0 Duration @0.050" ( Time-Area = 0.8932 Lift )
LSA = 112.982 degrees
* Specs adjusted for ValveTrain Deflection = 0.0000 Intake Lash= 0.0250 Exhaust Lash= 0.0250
* maximum Cam Specs required to achieve +900 Peak HP and higher than 900 Peak HP @ 7500 RPM

Cylinder Head Intake Port Flow @28 in. = 432.0000 -to- 462.6105 CFM at 0.97059 Lift (111.62117 Ve%)
Cylinder Head Exhaust Port Flow @28 in. = 310.1252 -to- 339.3970 CFM at 0.90592 Lift (no Flow Pipe)

"has a 2.23" intake valve (432 cfm @ .800")
and while I am correcting myself the exhaust valve is 1.72"

i realize you only want to use Blair's Equations/Methods !
i'd like to see how my Calcs compare to Blair's Methods ?
.... very interesting Thread !
.... waiting to see your Data results from Blair's methods

[DrillDawg]

BMEP is just a theoretical number that you use your torque output to figure, your measured torque output is a known, that's why no one uses BMEP any more, they use ftlbs\cuin or hp\cuin, even DV touts his ftlbs\cuin, lol.

[RevTheory]

Question: can one of these equations be used to calculate the best IVC for a target hp/rpm?

[Stan Weiss]

Stan,

The way I understand what you want to do is correct. The value is a "normalized" value and you have to "de-normalize" it for the specific engine you want to do the cam profile for.

I must admit I have never thought of doing it this way - very interesting!

One thing people seem to disregard about Blair - he was focused on designing an engine from scratch and giving the designer guidance to start with realistic values. The aim was not to wring the last 0.5% power out of an existing engine.

Vannik,
I believe this is how I would do steps 1 and 2. I still have step3 just rounding in my head.

Step 1 - TA1 = TA * (RPM * 6 / 1000)

Step 2 - TA2 = TA1 / (Intake Valve Diameter [Meter] * pi)

Stan

[Stan Weiss]

Stan
I am trying to use Blair's and time area.
Nowhere's does it need flow numbers.
Sorry, I just looked and the head I would use on this example
has a 2.23" intake valve (432 cfm @ .800")
and while I am correcting myself the exhaust valve is 1.72".

Stan ,
your Compression Ratio + VE% + Head CFM is already included ( sort of hidden inside )...
inside your desired 900 Peak HP at 7500 RPM
and inside your Peak TQ = 630.24 ( BMEP = 177.645 )

535 ci Pontiac engine for this example.
bore = 4.350", stroke = 4.500", rod = 6.700", cr = ??? (Pump gas), ( i used 10.25 and 11.0:1 CR )
Intake Valve = 2.230", Exhaust Valve = 1.720"

Maximum Head CFM @28in. = 431.99999455 to 462.61053223 CFM at 111.62117 % VE
Maximum Piston CFM = 962.46928032 occurs at 73.077765 degrees ATDC
Minimum recommended Flowbench Test Pressure = 62.4 inches vertical Manometer Water Column

Maximum Piston Velocity = 9325.689975 FPM occurs at 73.077765 degrees ATDC
Average Piston Velocity = 5625.000000 in Feet Per Minute
Piston Depth at 73.077765 degree ATDC= 1.950290 inches Cylinder Volume = 474.9729 CC
Crank Angle at which Rod and Crank axis form a 90 degree angle = 71.4368729 ATDC
Maximum TDC Rod Tension GForce = 4802.0155 G's Acceleration Ft/Sec^2 = 154500.2788
Maximum BDC Rod Compression GForce = 2387.5943 G's Acceleration Ft/Sec^2 = 76818.5744

i get these minimum Cam Specs : (* Race only Engine with 10.25:1 CR )
0.8617 = Intake Valve Lift 278.0 Duration @0.050"
0.8334 = Exhaust Valve Lift 298.0 Duration @0.050"
LSA = 108.118 degrees
* Specs adjusted for ValveTrain Deflection = 0.0000 Intake Lash= 0.0250 Exhaust Lash= 0.0250
.... * minimum Cam Specs required to achieve 900 Peak HP @ 7500 RPM

i get these maximum Cam Specs : (* Professional Race only Engine with 11.0:1 CR )
0.97059 = Intake Valve Lift 284.0 Duration @0.050" ( Time-Area = 0.9569 Lift )
0.90592 = Exhaust Valve Lift 300.0 Duration @0.050" ( Time-Area = 0.8932 Lift )
LSA = 112.982 degrees
* Specs adjusted for ValveTrain Deflection = 0.0000 Intake Lash= 0.0250 Exhaust Lash= 0.0250
* maximum Cam Specs required to achieve +900 Peak HP and higher than 900 Peak HP @ 7500 RPM

Cylinder Head Intake Port Flow @28 in. = 432.0000 -to- 462.6105 CFM at 0.97059 Lift (111.62117 Ve%)
Cylinder Head Exhaust Port Flow @28 in. = 310.1252 -to- 339.3970 CFM at 0.90592 Lift (no Flow Pipe)

"has a 2.23" intake valve (432 cfm @ .800")
and while I am correcting myself the exhaust valve is 1.72"

i realize you only want to use Blair's Equations/Methods !
i'd like to see how my Calcs compare to Blair's Methods ?
.... very interesting Thread !
.... waiting to see your Data results from Blair's methods

Larry,
Thanks for the input. If I ever get this to work. I also will be interested to see how the different method match up.

Stan

[Stan Weiss]

Question: can one of these equations be used to calculate the best IVC for a target hp/rpm?

Rev,
One of the equations tells what Time area we need for the cam segment from BDC to IVC.

Stan

[SchmidtMotorWorks]

Question: can one of these equations be used to calculate the best IVC for a target hp/rpm?

Not directly, it tells you how close your lift profile is to a set of target values.
When you find a lift profile that is close enough to the target then you get all of the timing values at once.
The aggressiveness of the profile will move the IVO, IVC etc.

Everyone reading this should be careful to understand there are two aspects to this system.

1. The concept of dividing the lift curves into regions and computing what is listed in the paper.
2. Setting the target values, the article provides a set of values that were fit to a small set of engines and those engines had a wide range; from garden tools to racing engines.
When the values for each of the engines are shown as points in a chart they do not form a straight line or even simple curve.
So the data was fit to the best approximation.

For someone that wants to use this for a particular engine type, they would begin by testing it and then comparing it to known engines that perform well. Then you would adjust the values in the formula to fit the result that you will want to duplicate in the future.

The key point to understand is that the concept of the system of how the engine is measured stays the same, the particular numbers will need to be refined for any particular type of work. For example the values that work for a Harley are unlikely to be precise for a 4 cylinder Japanese motorcycle engines.

Someone asked earlier, if it would be applicable to a particular engine with a particular manifold.
For a system to be capable of considering the intake manifold, the intake manifold needs to be an input to the system.
This system does not take engine duct dimensions so it does not consider them in the computation.
To some extent they are built in to the use of a performance metric like BMEP, because you need to use certain types of parts to accomplish a target BMEP.

If you want to have a system that does consider all of the intake, exhaust dimensions and more, then you need to step-up to a 1D software like EngMod4T authored by Vannik, who is posting in this thread.

http://vannik.co.za/

[Vincenzo]

Stan
if you wish to create a cam design that will compare closely with the STA's of your original post, it can be done fairly simply by generating a profile in EngMod4T, (see the screen shot of the relevant values, which are close enough for the purpose)
To convert these values into a file that can be read directly into Blair's 4StHead, Neels has a small program Cams4T which will convert the data into a MVL file, and from there a design file can be constructed.

As Neels has pointed out, the STA target values were only intended for use as a guide, and were never intended to be absolute 'musts'
A design to meet your original targets would involve a valve lift of 1" or thereabouts, and the mean piston speed based on your 7500 rom target would be right up at the high end of feasibility

[mk e]

2. Setting the target values, the article provides a set of values that were fit to a small set of engines and those engines had a wide range; from garden tools to racing engines.
When the values for each of the engines are shown as points in a chart they do not form a straight line or even simple curve.
So the data was fit to the best approximation.

For someone that wants to use this for a particular engine type, they would begin by testing it and then comparing it to known engines that perform well. Then you would adjust the values in the formula to fit the result that you will want to duplicate in the future.

You guys have mentioned this a couple times......I would think that is a deal breaker as it shows the work was incorrect and only produces a rough approximation that is 80-90% right at best.

If you want to have a system that does consider all of the intake, exhaust dimensions and more, then you need to step-up to a 1D software like EngMod4T authored by Vannik, who is posting in this thread.

http://vannik.co.za/

This really seems the the best input in the thread so far. Time has moved on, the days when simple equations that get you 80-90% there where really helpful are gone. A program like EngMod4T or Dymomation (that I use because its a bit simpler but less control) just makes "testing" your ideas so quick and painless, buying a copy was some of the best money I've ever spent. PipeMax is even cheaper and quicker...this it probably the best collection of equation solutions I've seen, again less flexible than the 1D sims but 5 minutes and you're in the right ballpark.

Sorry for the diversion, back to Bliar.

[Stan Weiss]

2. Setting the target values, the article provides a set of values that were fit to a small set of engines and those engines had a wide range; from garden tools to racing engines.
When the values for each of the engines are shown as points in a chart they do not form a straight line or even simple curve.
So the data was fit to the best approximation.

For someone that wants to use this for a particular engine type, they would begin by testing it and then comparing it to known engines that perform well. Then you would adjust the values in the formula to fit the result that you will want to duplicate in the future.

You guys have mentioned this a couple times......I would think that is a deal breaker as it shows the work was incorrect and only produces a rough approximation that is 80-90% right at best.

If you want to have a system that does consider all of the intake, exhaust dimensions and more, then you need to step-up to a 1D software like EngMod4T authored by Vannik, who is posting in this thread.

http://vannik.co.za/

This really seems the the best input in the thread so far. Time has moved on, the days when simple equations that get you 80-90% there where really helpful are gone. A program like EngMod4T or Dymomation (that I use because its a bit simpler but less control) just makes "testing" your ideas so quick and painless, buying a copy was some of the best money I've ever spent. PipeMax is even cheaper and quicker...this it probably the best collection of equation solutions I've seen, again less flexible than the 1D sims but 5 minutes and you're in the right ballpark.

Sorry for the diversion, back to Bliar.

Mark,
Most of the time you get what you pay.

What I am hoping to do is put a free entry level set of equations here for anyone to use. (The more I analyze this I am not sure that can be done). This I believe would cover many of the readers (lurkers) while the others as needed would buy the software packages you listed.

Stan

[SchmidtMotorWorks]

2. Setting the target values, the article provides a set of values that were fit to a small set of engines and those engines had a wide range; from garden tools to racing engines.
When the values for each of the engines are shown as points in a chart they do not form a straight line or even simple curve.
So the data was fit to the best approximation.

For someone that wants to use this for a particular engine type, they would begin by testing it and then comparing it to known engines that perform well. Then you would adjust the values in the formula to fit the result that you will want to duplicate in the future.

You guys have mentioned this a couple times......I would think that is a deal breaker as it shows the work was incorrect and only produces a rough approximation that is 80-90% right at best.

If you want to have a system that does consider all of the intake, exhaust dimensions and more, then you need to step-up to a 1D software like EngMod4T authored by Vannik, who is posting in this thread.

http://vannik.co.za/

This really seems the the best input in the thread so far. Time has moved on, the days when simple equations that get you 80-90% there where really helpful are gone. A program like EngMod4T or Dymomation (that I use because its a bit simpler but less control) just makes "testing" your ideas so quick and painless, buying a copy was some of the best money I've ever spent. PipeMax is even cheaper and quicker...this it probably the best collection of equation solutions I've seen, again less flexible than the 1D sims but 5 minutes and you're in the right ballpark.

Sorry for the diversion, back to Bliar.

This ^^^^ is exactly the process I use:

1. Run pipe max to get starting dimensions.

2. Run Dynomation to test it with some parts that I already have to see if they are not compatible, also try some what-if scenarios.

3. Run EngMod4T to confirm the results of Dynomation and test some things the Dynomation does not have inputs for.